3D Printed parts actually can be useful. If basic principles are observed when designing plastic parts, 3D Printed part can do a lot of work. For example, I took this part of the knuckle cord of my car. After the original part was broken, I wanted to try if I could to print the same part on my Da Vinci 3 in 1 3D Printer. I wanted this part to complete its role, because you can imagine how much force you have in a knuckle cord. Following the example of the broken part and using SolidWorks software package, I designed this part. In figure 1 you can see the render.
What I paid the most attention to was how to put it on a print bed to have the necessary strength, direction of laying the layers in terms of strength ( http://3dprintingcommunity.net/design-strong-3d-printable-parts/ ).
When setting up, I did not pay attention to where I would have a support. With 60% infill and 100 micron height of the layer I printed a part which actually does its work. Following are the pictures.